This invention relates to centrifuges for separation of a suspension with two liquid phases of different specific gravities to be removed separately.
A known centrifuge of this kind, in the form of a solid jacket decanter centrifuge as described in DE-PS No. 27 07 111, provides a simple apparatus for problem-free conversion between two-phase operation and three-phase operation. For two-phase operation where only one liquid phase is to be removed, all the openings to the receiving chamber which houses the skimmer mechanism are opened, while the radially-directed outlet openings are closed. A weir-barrier described below has been removed so that only the skimmer mechanism operates and draws off the liquid phase. For three-phase operation, i.e., if two liquid phases of different specific gravity must be removed separately, a portion of the openings are closed at their ends away from the separation chamber in the axial direction, and the outlet passages for these openings are opened. The weir-barrier is installed in such a way that the openings (connected as before with the receiving chamber which houses the skimmer mechanism) are connected with the separation chamber in a radially outward region, thus collecting the liquid phase of higher specific gravity while the other openings, with the aid of the weir-barrier, are connected with the separation chamber in an inner radial region, and thus collect the liquid phase of lower specific gravity, which is then conducted through associated outlet passages into a collector.
Centrifuges with skimmers, particularly those with radially adjustable skimmer heads, are among the high-quality decanter centrifuges for performing difficult separation tasks, for example, removing certain harmful products or waste products in a liquid phase. In such known centrifuges, the heavier liquid phase is conducted to the skimmer mechanism and removed by it, while the lighter liquid phase is spun off through the outlet openings. It is desirable to conduct the heavier liquid phase to the skimmer plate because the adjustability of the skimmer allows the centrifuge to be set to enable a clean separation. In such centrifuges, however, the removal of the lighter liquid phase over a weir-barrier leads to its being mixed with air. This is undesirable for some separations, specifically when the lighter liquid phase is sensitive, as is the case, for example, for volatile oils, other volatile materials, or oxidizable liquids. It therefore would be desirable to conduct the lighter liquid phase to the skimmer unit, and to be able to remove it under pressure, and thus to prevent mixing with air.